Motorized seat belt retractor

ABSTRACT

A motorized seat belt retractor having a load limiter to control the tensile load on a seat belt webbing, especially when the webbing is withdrawn due to an emergency condition. The load limiter controls the tension by controlling the condition of the motor that drives the retractor.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a divisional application of U.S.patent application Ser. No. 09/838,281 filed on Apr. 20, 2001 claimingpriority to and the benefit of U.S. Provisional Patent ApplicationSerial No. 60/198,751 filed Apr. 21, 2000. The foregoing applicationsare each incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a seat belt retractor with aload limiter and a locking mechanism. More particularly, the presentinvention relates to a retractor having a motorized load limiter andlocking mechansim.

[0003] Conventionally, retractors have include a mechanical load limitersuch as a torsion bar or the like for limiting the load applied on ashoulder or chest of an occupant of a motor vehicle. In theseconventional retractors the mechanical type of load limiter does notallow for the threshold setting for load on the webbing to be altered.Typically, the threshold value for the amount of tensile load to beapplied to the webbing is determined according to the model type ofautomobile. This threshold value is fixed and cannot be easily altered.

[0004] Therefore, it is desired to develop a novel retractor in whichthe threshold value for tensile load on the seat belt webbing isadjustable.

SUMMARY OF THE INVENTION

[0005] To achieve the aforementioned object, the present inventionprovides a motorized seat belt retractor having a load limiter forcontrolling the tensile load on a webbing withdrawn in the event ofemergency. The load limiter utilizes force generated by rotation of themotor shaft to control the tensile load. This approach to a load limiteris novel and may include a high-voltage motor having improved motorcurrent rising characteristics during starting of the motor.

[0006] According to the structure of the present invention, the forcegenerated by the rotation of the shaft of the motor can be utilized asthe tensile load for the load limiter. This configuration allows for theeasy adjustment of the threshold value of the tensile load on thewebbing and permits the threshold value to be set over a wider range ofpossible values.

[0007] The load limiter of the motorized seat belt retractor includes arotational resistance generating means which generates a rotationalresistance force in response to the rotation of the shaft of the motor.According to this structure, during rotation of the shaft of the motor arotational resistance force is generated due to the inertial moment ofthe shaft, this rotational resistance force can be positively utilizedto control the tensile load on the webbing.

[0008] In the aforementioned motorized seat belt retractor whichincludes a load limiter for controlling the tensile load on a webbingwithdrawn due to forward movement of an occupant in the event ofemergency, the load limiter includes a rotational resistance generatingmeans which provides for the generation of a rotational resistance forceby the motor when the motor is short circuited. According to thisstructure, the rotational resistance force generated by the motor whenshort circuited can be positively utilized as the tensile load for theload limiter, thereby eliminating the necessity of a separate mechanicalload limiter. Thus, the present invention provides for manufacturingmotorized seat belt retractors of a smaller size and at a low cost.

[0009] According to the present invention, the rotational resistancegenerating means of the motorized seat belt retractor generates arotational resistance force by switching the motor into either the shortcircuited state or the non-short circuited state according topredetermined sequence control. According to this structure, a desiredtensile load on the webbing can be obtained by suitably setting theperiod in which the motor is in the short circuited state and the periodin which the motor is in the non-short circuited state and sequentiallyswitching the short circuited state and the non-short circuited state ofthe motor.

[0010] In the motorized seat belt retractor, the non-short circuitedstate can mean that the motor is energized. According to this structure,the tensile load on the webbing can be controlled by utilizing therotational torque of the motor. The rotational resistance force of themotor in the non-short circuited state (i.e., energized state) isadjustable, thereby allowing a wider range for the setting value of thetensile load on the webbing.

[0011] In the motorized seat belt retractor, the non-short circuitedstate can mean that the motor is electrically connected via a resistor.According to this structure, the rotational resistance force of themotor in the non-short circuited state can be adjusted by changing theresistance value of the resistor, thereby allowing a wider range for thesetting value of the tensile load on the webbing.

[0012] In the motorized seat belt retractor, the non-short circuitedstate can mean that the motor is electrically open. According to thisstructure, little rotational resistance force is generated by the motorin the non-short circuited state when the motor is electricallydisconnected (open-circuit), thereby easily allowing a wider range forthe setting value of the tensile load on the webbing at a low costwithout any complex mechanism.

[0013] The load limiter of the motorized seat belt retractor includes agear train which couples the shaft of the motor to a spool on which thewebbing is wound. According to this structure, the tensile load on thewebbing can be controlled not only by adjusting the rotationalresistance force of the motor but also by changing the gear ratio of thegear train.

[0014] In the aforementioned rotational resistance generating meanswhich generates rotational resistance force by the motor, the rotationalresistance force further acts for preventing a rotational shaft of amotor from rotating in a direction of withdrawing the webbing. Accordingto this structure, the rotating shaft of the motor is electricallylocked, thus preventing rotation of the shaft at a suitable timing.

[0015] According to the present invention, described in general above,it is preferred that the rotational resistance force be generated atleast by counter-electromotive force generated by the rotation of therotational shaft of the motor when short circuited. According to thisstructure, the counter-electromotive force generated by the rotation ofthe rotational shaft of the motor when short circuited can be utilizedas the locking mechanism, thereby eliminating specific control fordriving the motor.

[0016] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only, and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features, aspects and advantages of the presentinvention will become apparent from the following description, appendedclaims, and the accompanying exemplary embodiments shown in thedrawings, which are briefly described below.

[0018]FIG. 1 is an exploded perspective view showing an embodiment of aretractor according to the present invention.

[0019]FIG. 2 is an explanatory view showing the mesh relation betweengears of the retractor of the embodiment according to the presentinvention.

[0020]FIG. 3a is a view illustrating a state where the motor is rotatedin the clockwise direction (CW direction) and

[0021]FIG. 3b is a view illustrating a state where the motor is rotatedin the counterclockwise direction (CCW direction).

[0022]FIG. 4 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point in this figure) to a point where the vehiclecompletely crashes. Curves indicate cases which are different in theweight (Light, Middle, Heavy) of occupant in the vehicle, respectively.

[0023]FIG. 5 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point in this figure) to a point where the vehiclecompletely crashes. Curves indicate cases which are different in thecollision speed (Low, Middle, High) of the vehicle, respectively.

[0024]FIG. 6a is a circuit diagram of the circuit including theretractor dc motor and a variable resistor.

[0025]FIG. 6b is a circuit diagram of the circuit including theretractor dc motor and a fuse.

[0026]FIG. 7 is a graph of the dc current/voltage applied to theretractor motor versus time.

DETAILED DESCRIPTION

[0027] Hereinafter, an embodiment of the present invention will now bedescribed with reference to the drawings. It should be understood thatthe sizes, shapes, positional relation of respective components areschematically shown just for understanding the invention and that thenumerical conditions stated in the following are just illustrativeexamples.

[0028] Hereinafter, an embodiment of a retractor according to thepresent invention will be described. FIG. 1 is an exploded perspectiveview showing the embodiment of the retractor according to the presentinvention. FIG. 2 is an explanatory view showing the mesh relationbetween gears of the retractor of this embodiment. It should be notedthat the illustration of a pyrotechnic pretension mechanism is omittedin FIG. 1.

[0029] The structure of the retractor of this embodiment will now bedescribed with reference to FIGS. 1, 2. The retractor 200 comprises thefollowing components: a retainer 20; a DC motor 21 attached integrallyto the retainer 20; a pinion 22 attached integrally to a motor shaft ofthe DC motor 21; a first gear 23 which is journalled by a projectionformed on the retainer 20 and is in mesh or engaged with the pinion 22.The first gear 23 is preferably an integral double gear comprising alarge gear 23 a and a small gear 23 b. The pinion 22 is positioned tomesh with the large gear 23 a.

[0030] The retractor also includes a second gear 24 which is journalledby a projection formed on the retainer 20 and is in mesh or engaged withthe first gear 23. In particular, the retainer is engaged with the smallgear 23 b. The second gear 24 is preferably an integral double gearcomprising a large gear 24 a and a small gear 24 b. The small gear 23 bis in mesh or engaged with the large gear 24 a.

[0031] The retractor further includes a third gear 25 which is in meshwith the second gear 24. In particular, the third gear is engaged withthe small gear 24 b. The third gear 25 is preferably an integral doublegear comprising a large gear 25 a and a small gear 25 b. The small gear24 b is in mesh with the large gear 25 a.

[0032] The retractor also includes three planetary gears 26 which are inmesh with the third gear 25. The planetary gears engage the small gear25 b. An internal gear 27 is also provided. The internal gear 27 hasinternal teeth 27 a which engage with the three planetary gears 26. Theinternal gear 27 includes external ratchet teeth 27 b formed in theouter periphery of the internal gear 27.

[0033] A pawl 30 is provided to engage with the external ratchet teeth27 b, and to thereby stop the rotation of the internal gear 27 in theclockwise direction. The pawl 30 is supported at a lever 31 comprising aspring at an end connected to the pawl 30. The other end of the lever 31includes a portion curled to form a ring member 32 that is formed in acurled portion of the other end of the lever 31. The ring member 32 iswound on a projecting disk-like member 33. The disk-like member 33 isintegrally formed coaxially with the first gear 23. A frictional piece34 projects from the outer periphery of the disk-like member 33 andpresses against the ring member 32 to apply friction.

[0034] The three planetary gears 26 are positioned on a carrier 35.Three pins 36 are provided for rotatably supporting and securing thethree planetary gears 26 to the carrier 35. A speed-reduction plate 37is interposed between the three pins 36 and the three planetary gears26.

[0035] A webbing W for restraining an occupant's body of which one endis fixed to a spool 38. As shown in FIGS. 2 and 3 arrow A designates adirection of withdrawing the webbing W and arrow B designates adirection of retracting the webbing W. The spool 38 includes a tipportion 38 a that passes through a rotational central hole of thecarrier 35. The tip portion 38 a also passes through the rotationalcentral hole of the third gear so as to be both slidable and rotatablerelative to the third gear. On the other hand, the root of the tipportion 38 a is fitted and fixed to the carrier 35.

[0036] The retractor includes a cover 39 covering the entire of theforce transfer mechanism or gear train. A plurality of screws 40 areprovided for fixing the cover 39 to the retainer 20.

[0037] A control circuit controls the connection of the DC motor 21 tobe short-circuited or non-short-ciruited and also controls the rotationof the DC motor 21 in the clockwise (CW) direction or in thecounterclockwise (CCW) direction.

[0038] As described herein, when the motor 21 is short circuited, nodriving current is supplied to turn the motor shaft. In this condition,when the shaft of the motor attempts to rotate due to the rotationalforce transferred from the first gear and engaged pinion a counterelectromotive force resists movement of the motor shaft.

[0039] As described herein, when the motor is non-short-circuited themotor may be located in an open-circuit or may be connected to a DCpower source which supplies a driving current that generates arotational force to drive the shaft in a chosen direction.

[0040] Hereinafter, description will now be made as regard to theoperation of the retractor of the present invention with theaforementioned components.

[0041] FIGS. 3(A) and 3(B) illustrating the operation of this embodimentwherein FIG. 3(A) is a view illustrating a state where the motor isrotated in the clockwise direction (CW direction) and FIG. 3(B) is aview illustrating a state where the motor is rotated in thecounterclockwise direction (CCW direction).

[0042] In the retractor 200, as shown in FIG. 2 and FIG. 3(B), theengaging pawl 30 is spaced apart from the external ratchet teeth 27 b sothat the internal gear 27 is not restricted in the normal state (i.e.,not in an emergency such as emergency braking or a vehicle collision).In this normal state, because of the property of the planetary geartrain, the rotational torque of the carrier 35 is not transmitted to thethird gear. Therefore, the rotational torque of the spool 38 integrallyfitted and fixed to the carrier 35 is not transmitted to the rotationalshaft of the DC motor 21, which is indirectly engaged with the thirdgear.

[0043] In the event of emergency, such as emergency braking and avehicle collision, a pretensioning mechanism (for winding up the webbingW to increase the tension prior to the pyrotechnic pretension mechanism)is actuated according to output signals from an ABS (anti-skid or brake)mechanism (not shown) and/or a collision predictive device (not shown)in order to rotate the rotational shaft of the DC motor 21 in the CWdirection as shown by the arrow in FIG. 3(A). Then, the rotationaltorque of the pinion 22 in the clockwise direction is transmitted to thefirst gear 23 as a rotational torque in the counterclockwise direction(indicated by arrow). As a result, the pawl 30 engages with one of theexternal ratchet teeth 27 b of the internal gear 27 to stop the rotationof the internal gear 27 in the clockwise direction (indicated by arrow).Therefore, the rotational torque of the third gear 25 can be transmittedto the carrier 35, which is integrally fitted and fixed to the spool 38.

[0044] In the case of the emergency condition, the rotational torque ofthe first gear 23 is transmitted to the second gear 24 as rotationaltorque in the clockwise direction (indicated by arrow). In addition, thetorque is further transmitted to the third gear 25 as rotational torquein the counterclockwise direction (indicated by arrow). Due to therotation of the third gear 25 in the counterclockwise direction, thesmall gear 25 b of the third gear 25 is rotated in the counterclockwisedirection so as to apply rotational torque in the clockwise direction(indicated by arrow) to the three planetary gears 26. The threeplanetary gears 26 rotate in the counterclockwise direction (indicatedby arrow) like planets around the small gear 25 b and, during thisrotation, engage with the internal teeth of the internal gear 27. Theinternal gear 27 is stopped from rotating by the pawl 30. Therefore, thecarrier 35 rotates to journal the three planetary gears 26 in thecounterclockwise direction (indicated by arrow). Because the spool 38 isfitted and fixed to the carrier 35, which is rotating in thecounterclockwise direction, the spool also rotates in the counterclockwise direction to wind up the webbing W (in the direction of arrowB).

[0045] Thereby, as described above, the rotational torque generated bythe shaft of the DC motor 21 rotating in the clockwise direction istransmitted to the spool 38 as rotational torque for winding up thewebbing W.

[0046] As impact is exerted on a vehicle body due to a vehiclecollision, impact detecting signals are outputted from an accelerationsensor (not shown) and/or a crush sensor (not shown) whereby apyrotechnic pretension mechanism (not shown) is actuated to retract thewebbing W into the retractor 200, as described above, thereby ensuringinitial restraint of the occupant.

[0047] After the collision or impact occurs, the webbing W will bewithdrawn (in a direction of arrow A in FIG. 3(A)) by the inertial forceof the occupant moving forwardly due to the collision. During thismovement of the webbing W and the spool 38, as shown in FIG. 3(A), thetorque applied to the spool 38 by withdrawing of the webbing W istransmitted to the DC motor 21 as rotational torque in thecounterclockwise direction (in a direction opposite to the direction ofarrow) because the engaging pawl 30 is engaged with the external ratchetteeth 27 b. When the DC motor is short-circuited (i.e., the terminalsare connected, but no external voltage is applied), the movement of theDC motor shaft created by the occupant's motion is opposed by a counterelectromotive force (“counter emf”). As a result, the motor shaftprovides a rotational resistance force that acts to prevent the rotationof the spool 38 and withdrawal of the webbing W.

[0048] The present invention provides for using the rotationalresistance force created by the rotating DC motor shaft to provide alocking mechanism and/or the EA mechanism. It should be noted that theterm “EA” is an abbreviation of “energy absorbing” meaning that impact(load) acting on an occupant's body is absorbed by a seat belt, and thisterm will be used generally hereinafter.

[0049] The characteristics of the rotational resistance force will nowbe described with reference to the drawings. FIG. 4 is a graphschematically showing the relation between the rotational resistanceforce F [Nm] (Newton meter) provided by the short-circuited DC motor andtime T [sec] (second) from a point where a vehicle collides with a wall(0 point of this graph) to a point where the vehicle completely crashes.The three curves shown in FIG. 4, indicate situations where differentweight occupants were located in the vehicle (i.e., Light, Middle andHeavy occupants).

[0050]FIG. 5 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point of this graph) to a point where the vehiclecompletely crashes or comes to rest. Curves indicate cases which aredifferent in the collision speed (Low, Middle, High) of the vehicle,respectively.

[0051] As shown in FIG. 4, in the case of a light-weight occupant, therising slope or inclination of the curve is relatively gentle (the solidline in the graph of FIG. 4). In the case of a heavy-weight occupant,the rising inclination of the curve is steep (the two-dot chain lineshown in FIG. 4). In the case of a medium-weight occupant, the risinginclination of the curve is middle between the case of the light-weightoccupant and the case of the heavy-weight occupant. Regardless of theoccupant's weight, the descending slope or inclination of all of thecases are gentle.

[0052] Accordingly, by using the rotational resistance force as the EAmechanism, EA load is relatively gently increased against thelight-weight occupant so that the total load on the light-weightoccupant is relatively small. On the other hand, EA load is relativelysteeply increased against the heavy-weight occupant so that the totalload on the heavy-weight occupant is relatively large. The decrease inEA load is gentle regardless of the occupant's weight, achieving “softlanding” (it means “decrease in belt tension acting on the occupant isgentle with time elapsing”).

[0053] As shown in FIG. 5, the higher the speed of the vehicle whencolliding with a wall, the higher the load limit of the rotationalresistance force F (EA load limit) (the two-dot chain line in the graphof FIG. 5). The lower the speed of the vehicle when colliding with awall, the lower the load limit of the rotational resistance force F (thesolid line in the graph of FIG. 5). That is, the load limit is increasedor decreased depending on the collision speed, exhibiting the idealoccupant restraint performance.

[0054] In case of conventional mechanical EA mechanism (e.g. a torsionbar) the rising inclination of EA load is constant so that the loadlimit is also constant regardless of the occupant's weight and thecollision speed. The present invention improves on conventional methodsand devices.

[0055] The load limit can be freely set in various manners as follows.For example, The gear ratio of the gears located between the shaft ofthe DC motor 21 and the web spool 38 may be changed. A change in gearratio changes the load limit of the rotational resistance forcetransmitted from the motor 21 to the spool 38. Also, a change in gearratio changes the rising and descending slope of the force over timeshown in FIG. 4.

[0056] Further by way of example, the DC motor 21 may be attached to acircuit that includes a variable resistor 40, as shown in FIG. 6a. Thevalue of the resistor 40 may be changed in order to change the loadlimit of the force being transferred from the motor to the web spool 38.Similarly, the value of resistance may be changed to adjust the risinginclination and the descending inclination of the curves shown in FIG.4. As the value of resistance is increased, the amount of forcetransferred from the motor 21 to the web spool 38 decreases. As aresult, the load limit decreases, the rising inclination becomesgentler, and the descending inclination becomes steeper. In this case, aplurality of resistors having different values of resistance may bepositioned in parallel and selectably connected to the circuit in such amanner as to automatically connect to a resistor having a value bestsuited to achieve ideal restraint performance.

[0057] Still further by way of example, a fuse 42 may be connected tothe power supply for the motor 21, as shown in FIG. 6b. The EA mechanismprovided by the motor 21 can be released by opening the fuse andopen-circuiting the motor to lower the EA load when current exceeds apredetermined value.

[0058] As described above, the DC motor 21 may be energized by a drivingcurrent to rotate in a direction for retracting the webbing W (thedirection of arrow in FIG. 3(A)). Rotation in this direction provides arotational resistance force opposite to the force provided by theoccupant. On the contrary, the rotational shaft of the DC motor 21 maybe rotated in the direction of withdrawing the webbing W (the directionopposite to the direction of arrow in FIG. 3(A)), to provide a forcethat subtracts from the conventional rotational resistance force.

[0059] The load limiter can also function as a locking mechanism, byproviding sufficient rotational resistance force to cancel therotational torque of the spool 38 acting in a direction of withdrawingthe seat belt.

[0060] Alternatively, the motor 21 may be replaced with another onehaving different output. Thus, the load limit of the rotationalresistance force F, the rising inclination, and the descendinginclination can be adjusted by changing the motor rating.

[0061] As shown in FIG. 7, the time period t1 of short circuit of the DCmotor 21 and the time period t2 of non-short circuit of the DC motor 21may be freely changed to make a pulse-like rectangular wave in order toadjust the load limit of the rotational resistance force F, the risinginclination, and the descending inclination of the resistance force. Forinstance, as the time period t1 is set longer than the time period t2,the load limit becomes higher, the rising inclination becomes steeper,and the descending inclination becomes gentler. On the contrary, as thetime period t2 is set longer than the time period t1, the load limitbecomes lower, the rising inclination becomes gentler, and thedescending inclination becomes steeper.

[0062] The timing for starting the EA mechanism can be controlled by anECU (“Electronic Control Unit”) for commanding the ignition timing of anairbag device or an ECU for a pretension mechanism.

[0063] It is preferable that the load limit of the rotational resistanceforce F, the rising inclination, and the descending inclination aresuitably set according to the withdrawal characteristic of webbing Wwhich is obtained from experiments using real cars with dummies.

[0064] A rotational shaft with a magnet in a copper tube may be usedinstead of the DC motor 21, thereby removing the requirement to energizethe motor and, thus, making EA mechanism at a low cost and with a simplestructure.

[0065] Combinations of the EA mechanism and various pretensionmechanisms such as a back pretensioner may provide more advantages.Further, a vehicle sensor may be incorporated in the retractor as an EAswitch.

[0066] The method of using the rotational resistance force of theshort-circuited motor as EA mechanism according to the present inventioncan be applied to a retractor of another type just like theaforementioned embodiment shown in FIG. 1.

[0067] As discussed above, the present invention achieves suitabletiming of locking.

[0068] Given the disclosure of the present invention, one versed in theart would appreciate that there may be other embodiments andmodifications within the scope and spirit of the invention. Accordingly,all modifications attainable by one versed in the art from the presentdisclosure within the scope and spirit of the present invention are tobe included as further embodiments of the present invention. The scopeof the present invention is to be defined as set forth in the followingclaims.

What is claimed is:
 1. A motorized seat belt retractor comprising: amotor having a motor shaft; a load limiter for controlling the tensileload on a webbing withdrawn in the event of emergency; wherein the loadlimiter is configured to utilize a force generated by the rotation ofthe motor shaft to thereby control the tensile load on the webbing.wherein the load limit is controlled using a fuse located in series withthe motor in an electrical circuit configured to carry a driving currentto the motor.
 2. The motorized seat belt retractor of claim 1, whereinthe fuse is configured to open at a predetermined value of current flowthrough the circuit to thereby open-circuit the motor and control theload limiter.
 3. The motorized seat belt retractor of claim 1, whereinsaid load limiter is configured to control the tensile load on thewebbing by alternatively placing the motor in a short-circuit andnon-short-circuit condition according to a predetermined sequence. 4.The motorized seat belt retractor of claim 3, further comprising anelectrical controller configured to establish the predeterminedsequence.
 5. The motorized seat belt retractor of claim 4, wherein thefuse is configured to open at a predetermined value of current flowthrough the circuit to thereby open-circuit the motor and control theload limiter.
 6. The motorized seat belt retractor of claim 1, whereinsaid load limiter includes a mechanism for transferring the forcegenerated by the rotation of the motor shaft to the webbing.
 7. Themotorized seat belt retractor of claim 6, wherein said mechanismcomprises a gear train which couples the shaft of the motor to a spoolon which the webbing is wound.
 8. The motorized seat belt retractor ofclaim 7, wherein said mechanism includes a locking mechanism to preventthe motor shaft from rotating in a direction corresponding to thewebbing being withdrawn.
 9. The motorized seat belt retractor of claim1, wherein the load limiter is configured to increase the forcegenerated by the motor at a rate determined based on the weight of avehicle occupant.
 10. The motorized seat belt retractor of claim 9,wherein the control device is an electrical controller.
 11. Theretractor of claim 10, wherein the load limiter only utilizes the forcegenerated by the motor.